From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4248DD7877D for ; Thu, 21 Nov 2024 15:23:14 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A0A2E6B007B; Thu, 21 Nov 2024 10:23:13 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 9BA5A6B0082; Thu, 21 Nov 2024 10:23:13 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 881F66B0083; Thu, 21 Nov 2024 10:23:13 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 69A2D6B007B for ; Thu, 21 Nov 2024 10:23:13 -0500 (EST) Received: from smtpin10.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 0F5F8161121 for ; Thu, 21 Nov 2024 15:23:13 +0000 (UTC) X-FDA: 82810468986.10.8F64EAA Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf20.hostedemail.com (Postfix) with ESMTP id 35C521C000A for ; Thu, 21 Nov 2024 15:22:03 +0000 (UTC) Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=Ppfws4NZ; spf=none (imf20.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=peterz@infradead.org; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1732202343; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=rxevy5h5i8g9QJaX9dDgnxXQcDraOey7eWADfayEl0k=; b=gs8a59Y8Q3Qf9Kr7VA5vhqF7JYiGIKaSNtqQOzuYjd9QvAy6/4OFUfYU92tgHGQIxDNc6U JdsUE0YOhU3d3ySoFgzXymXz3FXlBFmxfFhfmTuMywwRAitqMvop7U5o0T/zRF/R+KvKQ2 BSsrq/YZdyw9mHLhfpUTDvLeGE6KGk4= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=Ppfws4NZ; spf=none (imf20.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=peterz@infradead.org; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1732202343; a=rsa-sha256; cv=none; b=JN6vF1NBaba3Yp7HPmAB00n8B//17ywvmhzqxLdr7FCZIP+lkuj/DF3rhUe9MmOZ/51pgH sAtDE8pxaQnNPoRwtxX76v7whV7F67QVKUJw8hAr6As5NhsAT5CmZyAk/u6653Vjk9nZMX R2YAmaCSIwKnifR3hneAvAMjwjMReKg= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=rxevy5h5i8g9QJaX9dDgnxXQcDraOey7eWADfayEl0k=; b=Ppfws4NZ9w0ZwYZapvn7JbPIDU Kx1j9blrZQAcRovxmKXJHt0enTDoPvlAS+KHbSPE5wf3jxA24prNJXl4J1Q8/KixFx+qU4a7F4Jw5 uSxVL7lioES1lirZdA70En42ToKOskNdj4j3sHig07hRdlWIYOa2ci8X+BBGLnewQPM5Ph+mFOiek 7qzqpOeX8fiwwLudpnJsega7agLjvfb+Mv/9JVEBSs+zZPeRy6qMsSON84zTZqOmEbFvKiUkfN5qv AJ37nsW3ZgmrYdWR6QahOhkqj2+K9u70PACJIaVQs4CdCGdZcRM49kSmO3zhRpYg0NqVu9wtYWZ0C qL9W7Wkw==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1tE91F-00000006WEF-1bLS; Thu, 21 Nov 2024 15:22:58 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id B54E430068B; Thu, 21 Nov 2024 16:22:57 +0100 (CET) Date: Thu, 21 Nov 2024 16:22:57 +0100 From: Peter Zijlstra To: Andrii Nakryiko Cc: linux-trace-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, oleg@redhat.com, rostedt@goodmis.org, mhiramat@kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, jolsa@kernel.org, paulmck@kernel.org, willy@infradead.org, surenb@google.com, mjguzik@gmail.com, brauner@kernel.org, jannh@google.com, mhocko@kernel.org, vbabka@suse.cz, shakeel.butt@linux.dev, hannes@cmpxchg.org, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, david@redhat.com, arnd@arndb.de, richard.weiyang@gmail.com, zhangpeng.00@bytedance.com, linmiaohe@huawei.com, viro@zeniv.linux.org.uk, hca@linux.ibm.com, Thomas Gleixner Subject: Re: [PATCH v4 tip/perf/core 2/4] mm: Introduce mmap_lock_speculation_{begin|end} Message-ID: <20241121152257.GN38972@noisy.programming.kicks-ass.net> References: <20241028010818.2487581-1-andrii@kernel.org> <20241028010818.2487581-3-andrii@kernel.org> <20241121144442.GL24774@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241121144442.GL24774@noisy.programming.kicks-ass.net> X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 35C521C000A X-Stat-Signature: q6aft718y3i99pddn871g4i4os1pedeq X-Rspam-User: X-HE-Tag: 1732202523-884619 X-HE-Meta: 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 ux9p8HmF 8I5rGA2nGS89/DE4k40B8FN1iBTEztvOthEjR8PFgo/zcI1kFCyAmlQltAHQtmgaQMlcqWSLJZUsufPQRJ7bISO5PjrkKFnu+hGrzCulLT0g8gSaLmIM+vEcf1KH1d4dsiCrv31xr7kCePsPdPzc0LNXg/SY0cgub2Hlb9CHKU/AhyQZlbin4JjrTaNRIDMbtQ/j0BEdy/+C0VLBdbOxMpX5yaKzykJlp9VF41kZpc8qdKYUwf8eMHRzZpFfu5CLDrR8HeEbJlND6Cr3y2fWtbjBo+41QW/EPjQF9eXfm40s14US9E/kgdgpzTg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Nov 21, 2024 at 03:44:42PM +0100, Peter Zijlstra wrote: > But perhaps it makes even more sense to add this functionality to > seqcount itself. The same argument can be made for seqcount_mutex and > seqcount_rwlock users. Something like so I suppose. --- diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h index 5298765d6ca4..102afdf8c7db 100644 --- a/include/linux/seqlock.h +++ b/include/linux/seqlock.h @@ -318,6 +318,28 @@ SEQCOUNT_LOCKNAME(mutex, struct mutex, true, mutex) __seq; \ }) +/** + * raw_seqcount_try_begin() - begin a seqcount_t read critical section + * w/o lockdep and w/o counter stabilization + * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants + * + * Very like raw_seqcount_begin(), except it enables eliding the critical + * section entirely if odd, instead of doing the speculation knowing it will + * fail. + * + * Useful when counter stabilization is more or less equivalent to taking + * the lock and there is a slowpath that does that. + * + * If true, start will be set to the (even) sequence count read. + * + * Return: true when a read critical section is started. + */ +#define raw_seqcount_try_begin(s, start) \ +({ \ + start = raw_read_seqcount(s); \ + !(start & 1); \ +}) + /** * raw_seqcount_begin() - begin a seqcount_t read critical section w/o * lockdep and w/o counter stabilization